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RC circuit with dc current source

  1. Feb 22, 2009 #1
    1. The problem statement, all variables and given/known data
    Solve for the current in each branch of the following circuit as a function of time & derive and expression for the time dependence of teh emf of the constant current source in the circuit below.


    2. Relevant equations

    Zc = Xc = 1/(wC) = t/(2pi*C)


    3. The attempt at a solution

    I attempted to use the mesh method:

    Loop 1:
    -1000(i1)+50-(Zc)(i1)+(Zc)(i2)=0

    Loop 2
    -(Zc)(i2)+(Zc)(i1)-3500(i2)+3500(i3)=0

    Loop3:
    -3500(i3)+3500(i2)-5000(i3)-V=0

    This quickly got confusing when I substituted Zc for t/(2pi*120mF).
    I have no idea how to solve this problem when it has both a capacitor and a current source.

    I also do not understand what the second part of the question is asking.

    I would appreciate any help/insight that you could offer. Thanks.
     

    Attached Files:

  2. jcsd
  3. Feb 23, 2009 #2
    We can't see your picture until it's been approved, but I can tell you that for these kind of questions, usually, you have to either use differential equations or Laplace transformations. I assume you're familiar with one of them?

    The second part gets me too. I can understand each word separately, but put them together and it's jibberish to me. :blushing:
     
  4. Feb 23, 2009 #3

    Redbelly98

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    The 2nd part asks for the voltage across the current source, as a function of time.

    As a start, you could get the steady-state currents and voltages (t→∞).

    To solve this, I think we need some initial condition that isn't given. For example, perhaps the capacitor voltage is zero at t=0?
     
  5. Feb 23, 2009 #4
    That's all the information that I'm given. I have a feeling that since the current varies with time that I have to treat it like an ac circuit, and put in a function instead of i. I'm meeting with my prof today, so hopefully he provides some more insight.
     
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